1. Field of the Invention
The present invention relates to a float bath system for manufacturing a float glass and a cooling method of the same, and more particularly, to a float bath system for manufacturing a float glass which has an improved structure to cool a steel casing surrounding blocks for molten metal storage, and a cooling method of the same.
2. Description of the Related Art
Generally, an apparatus for manufacturing a float glass (also known as a sheet glass, a flat glass or a plate glass) using a float glass process is used to manufacture a continuous sheet of glass having a ribbon shape of a predetermined width by continuously supplying a molten glass onto a flowing molten metal (a molten tin and so on) stored in a float bath while floating the molten glass on the molten metal to form a molten glass ribbon reaching around an equilibrium thickness due to the surface tension and gravity, and pulling up the molten glass ribbon toward an annealing lehr near an exit of the float bath.
Here, the molten metal includes, for example, a molten tin or a molten tin alloy, and has a greater specific gravity than the molten glass. The molten metal is received in a float chamber where a reducing atmosphere of hydrogen (H2) and/or nitrogen (N2) gas is introduced. The float bath in the float chamber is configured to contain the molten metal therein. The float bath has a horizontally extending structure, and includes a high heat resistant material (for example, bottom blocks) therein. The molten glass forms a molten glass ribbon on the surface of the molten metal while moving from an upstream end of the float bath to a downstream end. The molten glass ribbon is lifted up at a location set on the downstream end of the float bath, so called a take-off point, to be removed from the molten metal, and delivered to an annealing lehr of a next process.
Meanwhile, the molten metal in the float chamber is maintained in a high-temperature state (for example, about 600 to 1100° C.), and a melting temperature of the molten metal (molten tin) is 232° C. Thus, it needs to cool down the bottom of the float bath to about 120 to 130° C. For this purpose, a conventional float bath system has an air blower for cooling a steel casing of the float bath by blowing an air to the lower surface of the steel casing.
However, if the operation of a driving source, for example a fan by which the air blower is driven, is suddenly stopped, it takes a considerable time to normalize the operation of the air blower. During the time the air blower is stopped, temperature of the bottom of the float bath increases, and consequently, tin existing around the bottom of the float bath returns into a liquid state and reacts with the steel casing, so that unnecessary alloys are formed and bubbles (O2) are created. In a severe instance, a hole may be generated in the steel casing, which should be replaced by a new steel casing.
Though a severe instance does not occur, contamination taking place during an abnormal operation as stated above changes the internal temperature of the float bath in the range of, for example −5° C. to +5° C. Such change in temperature changes the flow of molten metal, so that bubbles are created. This phenomenon causes surface defects (OBB (Open Bottom Bubble) or BOS (Bottom Open Seed)) of float glass products.